Hazard assessment, including evaluation of acute inhalation toxicity potential, is a mandatory international regulatory requirement for chemicals utilized in international commerce. Acute inhalation toxicity or irritation potential is an important consideration in establishing procedures for the safe handling, packaging and labeling and transport of chemicals and chemical mixtures, and in formulating responses to emergency exposure situations. Recently enacted legislation including the European Union (EU) Registration, Labeling and Authorization of Chemicals (REACH) program, and the US EPA High production Volume (HPV) Chemical Challenge will dramatically increase the need for inhalation toxicity information. The goal of the present grant proposal is to validate the EpiAirway in vitro human airway model for prediction of in vivo human inhalation toxicity hazard potential following Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) and European Center for Validation of Alternative Methods (ECVAM) guidelines. Phase I experiments produced several prediction models that will be further tested in the current Phase II project. One hundred chemicals that have available in vivo human or animal inhalation toxicity data and established immediately Dangerous to Life or health (IDLH) concentrations established by NIOSH will be utilized in the Phase II validation project. Interlaboratory transferability of the method will also be evaluated in 4 laboratories using a subset of 30 chemicals chosen from the original 100 tested during the Phase II study. The study data will then be submitted for independent statistical analysis and the final results and report will be submitted to regulatory agencies (i.e. ICCVAM) in support of regulatory acceptance. The technology to be validated in the current Phase II proposal will address a critical barrier to implementation of worldwide requirements for inhalation toxicity testing of chemicals, and a technical capacity that is urgently needed but that does not presently exist. The methodology developed will provide a transformative technology that will facilitate the paradigm shift from in vivo rodent to in vitro human inhalation toxicology testing envisioned in the resent National Research Council Report Toxicity Testing in the 21st Century: A Vision and a Strategy. PUBLIC HEALTH RELEVANCE: Hazard assessment, including evaluation of acute inhalation toxicity potential, is a mandatory international regulatory requirement for chemicals utilized in international commerce. Acute inhalation toxicity or irritation potential is an important consideration in establishing procedures for the safe handling, packaging and labeling and transport of chemicals and chemical mixtures, and in formulating responses to emergency exposure situations. The technology to be validated in the current Phase II proposal will address a critical barrier to implementation of worldwide requirements for inhalation toxicity testing of chemicals, and provide a technical capability that is urgently needed but that does not presently exist.